Anionic borate ligands and zwitterionic complexes formed therefrom

ABSTRACT

This invention provides an anionic borate ligand, and its synthesis. Zwitterionic complexes formed by the ligand and a metal, and Group 9 and 10 metals in particular, are described. Uses of the complexes in stoichiometric and catalytic reaction chemistry are also provided.

CROSS REFERENCE To RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication Serial No. 60/280,638 filed on Mar. 30, 2001.

FIELD OF THE INVENTION

[0002] This invention relates to anionic borate ligands, andbis(phosphino) and (bis(amino) borate ligands in particular. Theinvention further relates to zwitterionic complexes formed betweenanionic borate ligands and metals, such complexes finding utility innumerous stoichiometric and catalytic applications.

BACKGROUND OF THE INVENTION

[0003] Cationic, coordinatively unsaturated metal centers have played acritical role in the development of organometallic catalysis, andexhibit a wide range of both stoichiometric and catalytictransformations. Such species are frequently generated by methideabstraction with a strong Lewis acid, and they can also be generated byprotonation with an acid whose conjugate base is noncoordinating orweakly coordinating.

[0004] These cationic metal centers are amongst the most widely studiedsystems in organometallic research. Industrially importantpolymerization reactions often undergo key intermediary steps atcationic metal centers. With respect to transformations important toorganic synthesis, cationic late metal fragments enjoy widespread use inC—E bond forming processes, where E is C, N, O, S, Si, H, and so forth.Moreover, cationic metal centers are promising candidates for theultimate goal of selective activation and functionalization of lighthydrocarbon substrates.

[0005] However, in spite of the advances in the art, there continues tobe a need for improved methods of mediating reaction chemistry. Thepresent invention addresses those needs by a unique approach to thechemistry of cationic species whereby charge neutral zwitterionsincorporating a partially insulated borate counter-anion are used tomediate reaction chemistry related to their discrete cationic relatives.A review of the use of zwitterions in organometallic chemistry isdescribed in Chauvin et al., Eur. J Inorg. Chem. 577 (2000). Aside fromthe advantage of eliminating the need for a cocatalyst, there areseveral significant reactivity differences between the zwitterioniccomplex of the invention and traditionally cationic systems due to (i)differences in their relative electrophilicities, (ii) differences indonor ligand lability, and (iii) reduced or completely eliminatedion-pairing effects in the zwitterionic systems by comparison to theircationic counterparts. Further, solvents that dissolve ionic compoundsalmost always have polar, hence coordinating functional groups that canattenuate their reactivity. In principle, the zwitterionic complex ofthe invention will provide access to the chemistry of cationic metalcenters in relatively non-polar hydrocarbon media.

SUMMARY OF THE INVENTION

[0006] One aspect of the invention relates to compound having theformula:

[0007] wherein: R¹ and R² are independently selected from the groupconsisting of alkyl and aryl; Y is selected from the group consisting ofP and N; and R³, R⁴, R⁵ and R⁶ are independently selected from the groupconsisting of alkyl and aryl.

[0008] Another aspect of the invention pertains to a zwitterioniccomplex of the formula:

[0009] wherein: R¹ and R² are independently selected from the groupconsisting of alkyl and aryl; Y is selected from the group consisting ofP and N; R³, R⁴, R⁵ and R⁶ are independently selected from the groupconsisting of alkyl and aryl; Z is a metal; and R⁷ and R⁸ areindependently selected from the group consisting of halo, pseudo-halo,alkyl, aryl and mono or bidentate, displaceable neutral donor ligands.

[0010] Another aspect of the invention pertains to a zwitterioniccomplex of the formula III:

[0011] wherein: R¹ and R² are independently selected from the groupconsisting of alkyl and aryl; Y is selected from the group consisting ofP and N; R³, R⁴, R⁵ and R⁶ are independently selected from the groupconsisting of alkyl and aryl; Z is a metal; and R⁷ is selected from thegroup consisting of halo, pseudo-halo, alkyl, aryl and mono orbidentate, displaceable neutral donor ligands.

[0012] Yet another aspect of the invention relates to a method ofcatalyzing a reaction wherein transformation of a robust sigma bond inan organic compound is required, comprising: a) contacting the organiccompound with i) an organic or inorganic reagent, and ii) a zwifferioniccomplex of an anionic borate ligand having the formula:

[0013] and a metal compound; wherein: R¹ and R² are independentlyselected from the group consisting of alkyl and aryl; Y is selected fromthe group consisting of P and N; and R³, R⁴, R⁵ and R⁶ are independentlyselected from the group consisting of alkyl and aryl; and b) producingan organic compound having a transformed robust sigma bond.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention relates to anionic borate ligands, andbis(phosphino) and bis(amino) borate ligands in particular. Thesenegatively charged ligands can be installed on a variety of metalscenters, and Group 9 and 10 metals in particular, and are especiallyuseful for the preparation of neutral zwitterionic complexes. Thesezwitterionic complexes find utility in numerous applications instoichiometric and catalytic reaction chemistry reminiscent of theirdiscrete salt or ion-paired relatives. Examples of such applicationsinclude, by way of illustration and not limitation, benzene C—Hactivation processes (using platinum as the metal); catalytichydroaminations (using palladium as the metal); polymerizations such asthe copolymerization of ethylene and carbon monoxide (using palladium asthe metal); organic transformations; polymerizations; alkane activationand functionalization reactions such as in alkane oxidation; as well ashydrogenation, hydrosilation, and hydroboration (all using rhodium asthe metal).

[0015] The primary complex studied was a neutral platinum(II) alkylcomplex supported by the anionic bidentate phosphine ligand[Ph₂B(CH₂PPh₂)₂]. A lithium adduct of an anionic,bis(phosphino)aluminate species is described in Karsch et al.,Organometallics 4:231-238 (1985). The platinum system was examined forseveral reasons. First, C—H activation at Pt(II) metal centers iswell-established, particularly for systems with N-donor ligands. Incontrast, there are limited examples of intermolecular C—H bondactivation at platinum(II) centers supported by phosphine donor ligands:these phosphine-supported systems require relatively high temperatures(125-150° C.). It is expected that the zwitterionic, complexes describedherein, such as the bis(phosphino)borate platinum complexes, willpromote transformations at C—H bonds. Furthermore, it is expected thatsuch complexes will be soluble in relatively nonpolar media, in contrastto their discrete salt relatives Systems thus designed should beamenable to mechanistic study due to the presence of a usefulspectroscopic ³¹P NMR handle. In addition, designing systems thatattenuate or eliminate counter-anion effects may provide an importantmechanistic simplification.

[0016] Before describing detailed embodiments of the invention, it willbe useful to set forth definitions that are used in describing theinvention. The definitions set forth apply only to the terms as they areused in this patent and may not be applicable to the same terms as usedelsewhere, for example in scientific literature or other patents orapplications including other applications by these inventors or assignedto common owners. The following description of the preferred embodimentsand examples are provided by way of explanation and illustration. Assuch, they are not to be viewed as limiting the scope of the inventionas defined by the claims. Additionally, when examples are given, theyare intended to be exemplary only and not to be restrictive. Forexample, when an example is said to “include” a specific feature, thatis intended to imply that it may have that feature but not that suchexamples are limited to those that include that feature.

[0017] It must be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. Thus, forexample, reference to “a compound” encompasses a combination or mixtureof different compounds as well as a single compound, reference to“suitable solvent” includes a single such solvent as well as acombination or mixture of different solvents, and the like.

[0018] In describing and claiming the present invention, the followingterminology will be used in accordance with the definitions set outbelow.

[0019] As used herein, the term “alkyl” refers to a branched orunbranched saturated hydrocarbon group typically although notnecessarily containing about 1-24 carbon atoms, unless indicatedotherwise. Exemplary alkyl groups include methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, t-butyl, n-amyl, isoamyl, n-hexyl,n-heptyl, n-octyl, n-decyl, hexyloctyl, tetradecyl, hexadecyl, eicosyl,tetracosyl, and the like, as well as cycloalkyl groups such ascyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl,cyclooctyl and the like. Generally, although again not necessarily,alkyl groups herein contain about 1-12 carbon atoms. The term “loweralkyl” refers to an alkyl group of 1-6 carbon atoms, preferably 1-4carbon atoms. The alkyl group is optionally substituted at one or morepositions. Exemplary substituents include but are not limited tohydroxyl, cyano, alkoxy, ═O, ═S, —NO₂, halo, heteroalkyl, amine,thioether, —SH, and aryl. Accordingly, if not otherwise indicated, theterms “alkyl” includes branched, unbranched, unsubstituted, andsubstituted alkyl groups. The term “cycloalkyl” refers to a cyclicalkyl, as defined above, and is typically a stable 3-to 7 memberedmonocyclic or 7-to 10-membered polycyclic ring which is saturated orpartially unsaturated (e. g., containing one or more double bonds).Similarly, the term “cycloheteroalkyl” is intended to mean a cyclicalkyl group, as defined above, that contains one or more heteroatoms,and is typically a stable 3-to 7 membered monocyclic or 7-to 10-memberedpolycyclic ring which is saturated or partially unsaturated and contains1-4 heteroatoms (N, O, S, P or Si). As with alkyl, the terms“cycloalkyl” and “cycloheteroalkyl” are intended to include bothunsubstituted and substituted groups. The substitutions can be on acarbon or a heteroatom if the resulting compound is stable. For example,any amino group contained within the heterocycloalkyl group can be aprimary, secondary or tertiary amine, as long as the structure isstable.

[0020] As used herein, the term “aryl” is intended to mean an aromaticsubstituent containing a single aromatic ring (e.g., phenyl) or multiplearomatic rings that are fused together (e.g., naphthyl or biphenyl),directly linked, or indirectly linked (such that the different aromaticrings are bound to a common group such as a methylene or ethylenemoiety). Typically, the aryl group comprises from 5-14 carbon atoms.Preferred aryl groups contain one aromatic ring or two fused or linkedaromatic rings, e.g., phenyl, naphthyl, biphenyl, diphenylether,diphenylamine, benzophenone, and the like. The aryl moiety may beindependently substituted with one or more substituent groups, typically1-3 substituents, including ═O, —OH, —COOH, —CH₂—SO₂-phenyl, —C₁₋₆alkyl,—O—C₁₋₆alkyl, —C(O)—C₁₋₄alkyl, —(CH₂)₀₋₂—C(O)—O—C₁₋₄alkyl, cycloalkyl,—C₁₋₆alkoxy, halo, nitro, amino, alkylamino, dialkylamino,—C(O)—N(C₁₋₄alkyl)₂, —NH—C(O)—C₁₋₄alkyl, —C(O)—NH₂, —SO₂—NH₂,trifluoromethyl, cyano, aryl, benzyl, —O—aryl and —S—aryl. Thus, theterm “aryl” includes unsubstituted and substituted aryl groups. The term“heteroaryl” refer to aryl, as defined above, in which at least onecarbon atom, typically 1-3 carbon atoms, is replaced with a heteroatom(N, O, S, P or Si). The heteroaryl can have the heteroatoms within asingle ring, (e.g., such as pyridyl, imidazolyl, thiazolyl, pyrimidine,oxazolyl, and the like), or within two rings (e.g., indolyl, quinolinyl,benzofuranyl, and the like). As with aryl, the term “heteroaryl” isintended to include both unsubstituted and substituted heteroarylgroups. The substitutions can be on a carbon or a heteroatom if theresulting compound is stable. For example, any amino group containedwithin the heteroaryl group can be a primary, secondary or tertiaryamine, as long as the structure is stable.

[0021] The term “halo” is intended to represent a chloro (Cl), bromo(Br), fluoro (F) or iodo (I) substituent.

[0022] The term “heteroatom” refers to nitrogen, oxygen, sulfur,phosphorus and silicon. As a linker, the heteroatom is represented by—O—, —S—, —NR—, etc. The heteroatoms can exist in their chemicallyallowed oxidation states. Thus sulfur can exist as a sulfide, sulfoxide,or sulfone.

[0023] The term “ligand or the abbreviation “L” refers to a mono orbidentate, displaceable neutral donor ligand. Examples of such ligandsinclude by way of illustration an not limitation, acetone, acetonitrile,olefin adducts, carbon monoxide, pyridine, tertiary phosphines, tertiaryamines, diethyl ether, and so forth.

[0024] The term “pseudo-halide” or “pseudo-halo” refers to thosecompounds or substituents that behave as halides in their acid-base andredox chemistry. These include, by way of example, triflate(R—O—S(O)₂CF₃), acetates (R—O—C(O)CH₃), trifluoroacetate (R—O—C(O)CF₃),azide, cyanide and so forth.

[0025] In describing and claiming the present invention, the followingabbreviations will be used in accordance with the definitions set outbelow. Ar aryl ASN 5-azonia-spiro[4.4]nonane ASNBr 5-azonia-spiro[4.4]nonane bromide n-BuLi n-butyllithium t-Bu tert-butyl CODcyclooctadiene DABCO 1,4-diazabicyclo[2,2,2]octane DCM dichloromethanedppp 1,3-bis(diphenylphosphino)propane) Et ethyl Et₂O diethyl ether Et₃Ntriethylamine EtOH ethanol L mono or bidentate, displaceable neutraldonor ligand Me methyl NBD norbornadiene OTf —O—S(O)₂CF₃ Ph phenylPh₂BCl diphenylchloroborane RT room temperature THF tetrahydrofuranTMEDA N,N,N′,N′-tetramethylethylene-1,2-diamine

[0026] One embodiment of the invention is a class of anionic borateligands, which are compounds having the formula I:

[0027] wherein:

[0028] R¹ and R² are independently selected from the group consisting ofalkyl and aryl;

[0029] Y is selected from the group consisting of P and N; and

[0030] R³, R⁴, R⁵ and R⁶ are independently selected from the groupconsisting of alkyl and aryl.

[0031] Exemplary compounds of formula I are described below. This listis intended to be illustrative and not limiting of the invention. Thecompounds are shown as R¹ and R² being the same substituent, and the R³,R⁴, R⁵ and R⁶ substituents being the same. It is understood however,that the invention also encompasses those compounds where R¹ and R² aredifferent from each other, and the R³, R⁴, R⁵ and R⁶ substituents aredifferent from each other. TABLE 1 Compound R¹ and R² Y R³, R⁴, R⁵ andR⁶ (I)1 phenyl P phenyl (I)2 3-methylphenyl P phenyl (I)33-t-butylphenyl P phenyl (I)4 3-methoxyphenyl P phenyl (I)52,4-di(trifluoromethyl)- P phenyl phenyl (I)61,2,3,4,5-pentafluorophenyl P phenyl (I)7 phenyl-d₅ P phenyl (I)8 phenylP t-butyl (I)9 3-t-butylphenyl P t-butyl (I)10 phenyl P methyl (I)11phenyl P 3-t-butylphenyl (I)12 phenyl P 2,4-di(trifluoromethyl)- phenyl(I)13 phenyl N methyl (I)14 phenyl N isopropyl (I)15 phenyl N t-butyl(I)16 phenyl N phenyl

[0032] The bis(phosphino) and bis(amino) borate ligands of the inventioncan be installed on a variety of metals centers. Accordingly, anotherembodiment of the invention pertains to a zwitterionic complex of theformula II:

[0033] wherein:

[0034] R¹ and R² are independently selected from the group consisting ofalkyl and aryl;

[0035] Y is selected from the group consisting of P and N; and

[0036] R³, R⁴, R⁵ and R⁶ are independently selected from the groupconsisting of alkyl and aryl;

[0037] Z is a metal; and

[0038] R⁷ and R⁸ are independently selected from the group consisting ofhalo, pseudo-halo, alkyl, aryl and mono or bidentate, displaceableneutral donor ligands.

[0039] Metals suitable for use in the zwitterionic complex of theinvention include, by way of example and not limitation, metals fromGroup 4 of the Periodic Table of the Elements (titanium (Ti), zirconium(Zr), hafnium (HF)), from Group 7 of the Periodic Table of the Elements(manganese (Mn), rhenium (Re)), from Group 8 of the Periodic Table ofthe Elements (iron (Fe), ruthenium (Ru), osmium (Os)), from Group 9 ofthe Periodic Table of the Elements (cobalt (Co), rhodium (Rh), iridium(Ir)), from Group 10 of the Periodic Table of the Elements (nickel (Ni),palladium (Pd), platinum (Pt)), and aluminum (Al), can be used in thecomplex of the invention. Metals from Group 9 and Group 10 areparticularly preferred, in particular, rhodium, nickel, palladium, andplatinum.

[0040] Exemplary compounds of formula II are described below. This listis intended to be illustrative and not limiting of the invention. Forcompounds (II)1-12, R¹ and R² are phenyl; R³, R⁴, R⁵ and R⁶ are phenyl;and Y is P. For compound (II)13, R¹ and R² are phenyl; R³, R⁴, R⁵ and R⁶are methyl; and Y is N. TABLE II Compound Z R⁷ R⁸ (II)1 Ni chloro chloro(II)2 Ni methyl chloro (II)3 Ni chloro L (II)4 Ni L L (II)5 Pd or Ptchloro chloro (II)6 Pd or Pt methyl methyl (II)7 Pd or Pt R chloro (II)8Pd or Pt R L (II)9 Pd or Pt L L (II)10 Pd or Pt -O-acetyl -O-acetyl(II)11 Pd or Pt OTf OTf (II)12 Pd or Pt OTf L (II)13 Rh L L

[0041] Another embodiment of the invention pertains to a zwitterioniccomplex of the formula III:

[0042] wherein:

[0043] R¹ and R² are independently selected from the group consisting ofalkyl and aryl;

[0044] Y is selected from the group consisting of P and N; and

[0045] R³, R⁴, R⁵ and R⁶ are independently selected from the groupconsisting of alkyl and aryl;

[0046] Z is a metal; and

[0047] R⁷ is selected from the group consisting of halo, pseudo-halo,alkyl, aryl and mono or bidentate, displaceable neutral donor ligands.

[0048] Exemplary compounds of formula III are described below. This listis intended to be illustrative and not limiting of the invention. Forall of the foregoing examples, R¹ and R² are phenyl; R³, R⁴, R⁵ and R⁶are phenyl; and Y is P. TABLE III Compound Z R⁷ (III)1 Pd or Pt chloro(III)2 Ni methyl (III)3 Rh L

[0049] As noted above, the zwitterionic complexes of the invention findutility in numerous stoichiometric and catalytic applications, as willbe described in detail below. Accordingly, one aspect of the inventionis a method of catalyzing a reaction wherein transformation of a robustsigma bond in an organic compound is required, comprising: a) contactingthe organic compound with i) an organic or inorganic reagent, and ii) azwitterionic complex of an anionic borate ligand having the formula:

[0050] and a metal compound; wherein: R¹ and R² are independentlyselected from the group consisting of alkyl and aryl; Y is selected fromthe group consisting of P and N; and R³, R⁴, R⁵ and R⁶ are independentlyselected from the group consisting of alkyl and aryl; and b) producingan organic compound having a transformed robust sigma bond.

[0051] The robust sigma bond is an E—H bond, where E is C, B, Si, N, Hor O. Thus, the organic compound used in the method will be a compoundhaving at least one robust sigma bond, such as R—C—H, R—B—H, R—Si—H,R—N—H, H—H or R—O—H. The robust sigma bond is preferably a C—H bond.

[0052] It is expected that the zwitterionic complex of the inventionwill be useful in mediating transformations similar to their moretraditional cationic relatives. The following reaction transformationsare intended to be merely illustrative and not limiting of theapplications to which these complexes can be utilized. The followingtransformations were selected because they rely upon many elementaryorganometallic processes including (i) solvent ligand dissociation, (ii)oxidative addition, (iii) olefin insertion, (v) β-hydride elimination,(vi) and reductive elimination. As the zwitterion of the invention hasproved to be competent at mediating these reactions, comparative ratedata between the zwitterion of the invention and their structurallyrelated cations is obtainable.

Benzene C—H Activation

[0053] In one embodiment of the invention, the zwitterionic complex isused to mediate a benzene C—H activation process. Exemplary C—H bondactivation reactions are shown below.

[0054] The term electrophilic activation has been widely used todescribe a variety of late metal complexes that mediate C—H bondactivation processes (Stahl at al., Angew. Chem. Int. Edit. 37: 2181(1998)). An important issue to be resolved is whether these cationicsystems mediate C—H activation processes because they are highlyelectrophilic, or simply because they have an exposed coordination site.A charge neutral, zwitterionic platinum(II) system supported by the[Ph₂B(CH₂PPh₂)₂]⁻ ligand (Thomas et al., J. Am. Chem. Soc. 123:5100(2001), as well as a cationic complex supported by Ph₂Si(CH₂PPh₂)₂, wereprepared to address this question.

[0055] The main results are summarized as follows. Both the chargeneutral platinum complex [Ph₂B(CH₂PPh₂)₂]Pt(Me)(THF) and the cationiccomplex [Ph₂Si(CH₂PPh₂)₂]Pt(Me)(THF)] [B(C₆F₅)₄] mediated a clean,pseudo-first order benzene C—H activation reaction at moderatetemperature (˜45° C.). Few phosphine-supported platinum(II) systems havebeen studied with respect to C—H activation processes; those that havebeen studied require much higher temperatures (˜125° C.). For a relatedcationic system that requires high temperatures (>120° C.), see Peterset al., Organometallics 17:4493 (1998). Most significant is that thecharge neutral zwitterionic complex of the invention mediates the bondactivation reaction at an appreciably faster rate (˜10-fold). Thezwitterion shows a rather small deuterium isotope effect(k_(H)/k_(D)=1.25), clean pseudo-first order kinetics(k_(obs)=1.42(5)×10 ⁻⁴s⁻¹ at 45° C.; t_(½)=81 minutes), and a large THFdependence. These data are consistent with a rate-limiting stepdependent on THF loss. Kinetic studies of the cationic system revealed amuch larger deuterium isotope effect (k_(H)/k_(D)=6.10). The distinctlydifferent isotope effects observed may indicate that differentrate-determining steps are operative in each system; oxidative C—H bondaddition, rather than solvent loss, may be rate-determining in thecationic system.

[0056] This experiment suggests that electrophilic C—H activation maynot be the best description for a C—H activation process mediated byplatinum(II), at least for phosphine donor ligand systems. Studies ofcationic dimmine platinum complexes indicate that a more electron-richcomplex will mediate a benzene C—H activation process at a faster rate(Zhong et al., J. Am. Chem. Soc. ___:___(2002) inpress).

Polymerization

[0057] In another embodiment of the invention, the zwitterionic complexis used to catalyze a polymerization reaction. For example, thepolymerization reaction can be the copolymerization of ethylene andcarbon monoxide to yield —[(CH₂)₂—(CO)]_(n)—.

[0058] It is known that cationic palladium(II) complexes supported bychelating phosphines are able to mediate the strictly alternatingcopolymerization of carbon monoxide and ethylene to generate polyketonepolymer (Drent et al., Chem. Rev. 96:663 (1996)). The zwitterions of theinvention also mediate this polymerization reaction.

[0059] [Ph₂B(CH₂PPh₂)₂]Pd(Me)(THF) was prepared and its reactivitymeasured under a pressure of CO and ethylene. This system serves as acharge neutral relative to the prototypical, cationic catalyst system[(dppp)Pd(Me)(solv)]⁺. The zwitterionic Pd(II) complex,[Ph₂B(CH₂PPh₂)₂]Pd(Me)(THF), was found to be a very active catalyst forthe copolymerization of CO and ethylene at ambient temperature andafforded clean, strictly alternating polyketone (MW˜138,000; Mn˜112,000;PDI=1.25). In a comparative study this zwitterion was shown to be asefficient a catalyst as structurally related cationic systems, asreported in Lu et al., J. Amer. Chem. Soc. ___:___(2002) in press.

[0060] The olefin adduct [Ph₂B(CH₂PPh₂)₂]Pd(CH₃)(CH₂=CH₂) can be formedcleanly at low temperature under excess ethylene. Its first order decaywas measured to compare its rate of ethylene insertion with[(dppp)Pd(Me)(CH₂═CH₂)][B(3,5-(CF₃)₂—C₆H₃)₄]. Within experimental error,the insertion rate obtained for [Ph₂B(CH₂PPh₂)₂]Pd(CH₃)(CH₂═CH₂) wasequal to that reported for [(dppp)Pd(Me)(CH₂═CH₂)][B(3,5-(CF₃)₂—C₆H₃)₄]at −47° C. in CH₂Cl₂. This result is surprising given the presumeddifference in electrophilicity between the two systems. Moreover, thisexperiment introduces the notion that the zwitterions of the inventionmay serve to mediate rapid olefin insertion rates when cationic,isostructural complexes are already known to do so.

Catalytic Addition of H—E Bonds to Olefins and Alkynes

[0061] In another embodiment of the invention, the zwitterionic complexis used to catalyze the addition of E—H bonds to olefins and alkynes,where the E—H bond is selected from the group consisting of H—H, Si—H,B—H, C—H, and N—H. Three exemplary E—H addition reactions to olefins areillustrated below.

[0062] A series of zwitterionic complexes including the phosphine-basedsystems [Ph₂B(CH₂PPh₂)₂]Rh(norbornadiene) and[Ph₂B(CH₂PPh₂)₂]Rh(solvent)₂, and the nitrogen-based systems [Ph₂BN^(Me)₂]Rh(norbornadiene) and [Ph₂BN^(Me) ₂]Rh(solvent)₂ were prepared. Thesesystems give rise to rapid catalytic processes including hydrogenation,hydrosilation, hydroboration, and hydroacylation reactions (see above),transformations also mediated by their traditional cationiccounter-parts. Interestingly, the neutral zwitterions are activecatalysts even with acetonitrile as the solventodonor ligand:Acetonitrile typically poisons cationic systems by tying up a requiredsubstrate coordination site (Bosnich et al., Acc. Chem. Res. 31:667(1998)). For example, the zwitterionic complex[Ph₂B(CH₂PPh₂)₂]Rh(CH₃CN)₂ rapidly hydroacylates 4-methyl-4-pentenal toquantitatively produce 3-methylcyclopentanone as a racemic mixture (0.2mol % catalyst, THF, 25° C., 30 min). The related cationic systems[Ph₂Si(CH₂PPh₂)₂and [Ph₂Si(CH₂PPh₂)₂Rh(acetone)₂][B(C₆F₅)₄] show verypoor activity under similar conditions;[Ph₂Si(CH₂PPh₂)₂Rh(CH₃CN)₂][B(C₆F₅)₄] is completely inactive while[Ph₂Si(CH₂PPh₂)₂Rh(acetone)₂][B(C₆F₅)₄] is extremely sluggish, even at25 mol %.

[0063] These results suggest that the zwitterionic complex of theinvention systems is likely to be less sensitive to polar donor solventsor functionalities that might otherwise attenuate, or completelyinhibit, catalytic activity in typical cationic systems.

Selective Activation of SP³-Hybridized Bonds

[0064] In another embodiment of the invention, the zwitterionic complexis used to selectively activate sp³-hybridized C—H bonds. This isillustrated below for the selective activation of sp³-hybridized C—Hbonds α to tertiary amine N atoms.

[0065] In the course of exploring amine base “promoted” strategies toC—H bond activation chemistry at platinum, it was found that thezwitterionic complex [Ph₂B(CH₂PPh₂)₂]Pd(OTf)(THF), which in THFequilibrates with the disolvento species [Ph₂B(CH₂PPh₂)₂]Pd(THF)2][OTf],underwent a C—H bond activation reaction 60° C. with tertiary amines tocleanly generate a novel organometallic product in which the carbon atomα to the amine nitrogen had lost a proton and was replaced by palladium.A stoichiometric equivalent of ammonium triflate was trapped in thereaction. Most intriguing was the selectivity of the C—H activationprocess for sp³-hybridized C—H bonds a to a tertiary amine.

[0066] It is expected that the zwitterionic complex will also serve tocatalyze the procedure for functionalizing tertiary amines at the a C—Hposition.

Organic Transformation

[0067] In another embodiment of the invention, the zwitterionic complexis used to catalyze an organic transformation reaction. The examples setforth above fall into this category, such as the catalytic addition ofE—H bonds to olefins and alkynes.

Alkane Activation

[0068] In another embodiment of the invention, the zwitterionic complexis used to catalyze an alkane activation reaction. Examples of suchreactions include palladium and platinum catalyzed C—H activationreactions.

Alkane Functionalization

[0069] In another embodiment of the invention, the zwitterionic complexis used to catalyze an alkane functionalization reaction. An example ofan alkane functionalization reaction is an alkane oxidative reaction.

[0070] In addition to the reactions described above, the zwitterioniccomplex of the invention finds utility in the improved synthesis ofnumerous compounds, and pharmaceutical agents in particular, that aresynthesized by methods utilizing traditional metal catalysts such as aPd—C catalyst, a Raney-Ni catalyst, a Pt catalyst, a Pd—C catalyst, andso forth.

EXAMPLES

[0071] The practice of the present invention will employ, unlessotherwise indicated, conventional techniques of pharmaceuticalformulation, medicinal chemistry, and the like, which are within theskill of the art. Such techniques are explained fully in the literature.

[0072] The following examples are put forth so as to provide those ofordinary skill in the art with a complete disclosure and description ofhow to make and use the compounds of the invention, and are not intendedto limit the scope of what the inventors regard as their invention.Efforts have been made to ensure accuracy with respect to numbers (e.g.,amounts, temperature, etc.) but some errors and deviations should beaccounted for. Unless indicated otherwise, parts are parts by weight,temperature is in ° C. and pressure is at or near atmospheric. Allcomponents were obtained commercially unless otherwise indicated.

Materials and Methods

[0073] Unless otherwise noted, all syntheses were carried out in theabsence of water and dioxygen, using standard Schlenk and gloveboxtechniques. THF, Et₂O, petroleum ether, DCM, acetonitrile, toluene, andbenzene were deoxygenated and dried by thorough sparging with N₂ gasfollowed by passage through an activated alumina column and were storedover 3 Å molecular sieves. For the Pt compounds, pentane, hexanes, andEtOH were deoxygenated by repeated evacuation under reduced pressurefollowed by introduction of dinitrogen and were dried by storing over 3Å molecular sieves. For the Rh compounds, EtOH and methanol weredistilled under vacuum after stirring over CaH₂ for 24 h. Nonhalogenatedsolvents were typically tested with a standard solution of sodiumbenzophenone ketyl in tetrahydrofuran in order to confirm effectiveoxygen and moisture removal. Deuterated chloroform, benzene, DCM,acetonitrile, and acetone were purchased from Cambridge IsotopeLaboratories, Inc. and were degassed by repeated freeze-pump-thaw cyclesand dried over activated 3 Å molecular sieves prior to use. B(C₆F₅)₃ wasrecrystallized from pentane at −35 ° C. prior to use. (COD)Pt(Cl)₂(Clark et al., J. Organomet. Chem 59:411-428 (1973)), (COD)Pt(Me)(Cl)(Clark et al., J. Organomet.Chem59:411-428 (1973)), (COD)Pt(Me)₂ (Costaet al., M.Inorg.Syn.31:284-286 (1995)), Ph₂BCl (Treichel et al.,Inorg.Syn. 13:32-38 (1973)), Ph₂PMe (Seyferth et al., J.Org.Chem.28:2463-2464 (1963)), Ph₂PCH₂Li(TMEDA) (Schore et al., Inorg.Chem. 20:3200-3208 (1981)), and 5-azonia-spiro [4,4]nonane bromide(Blicke et al., J. Org. Chem. 76:5099-5103 (1954)) were prepared by thenoted literature methods.

[0074] [^(i)Pr₂EtNH][BPh₄] was prepared by acidifying an aqueoussolution of ^(i)Pr₂EtN and NaBPh₄with aqueous HCl. (COD)Pt(Me)(Ph)(Clark et al., J. Organomet. Chem. 101:347-358 (1975); Hackett et al.,Organometallics 6:403-410 (1987)) was prepared by addition of PhMgBr toa cold (−35° C.) DCM solution of (COD)Pt(Me)(Cl). All other chemicalswere purchased from Aldrich, Strem, Alfa Aesar, or Pressure Chemicalsand used without further purification.

[0075] NMR spectra were recorded at ambient temperature on VarianMercury 300 MHz and Inova 500 MHz, and Joel 400 MHz spectrometers,unless otherwise noted. ¹H and ¹³C NMR chemical shifts were referencedto residual solvent. For the Pt compounds, ³¹P NMR and ¹¹B NMR chemicalshifts are reported relative to an external standard of 85% H₃PO₄ orneat BF₃.Et₂O respectively. For the Rh compounds, ³¹P NMR, ¹¹B NMR, and¹⁹F NMR chemical shifts are reported relative to an external standard of85% H₃PO₄, neat BF₃.Et₂O, and neat CFCl₃ respectively. IR spectra wererecorded on a Bio-Rad Excalibur FTS 3000 spectrometer controlled byWin-IR Pro software. Elemental Analyses were performed by DesertAnalytics, Tucson, Ariz. X-ray diffraction experiments were carried outby the Beckman Institute Crystallographic Facility on a Bruker Smart1000 CCD diffractometer. MS data for samples were obtained by injectionof an acetonitrile solution into a Hewlett Packard 1100MSD MassSpectrometer (ES+) or an Agilent 5973 Mass Selective Detector (EI).Deuterated solvents were degassed and dried over activated 3-Å molecularsieves prior to use.

General Method for Preparation of Borane Synthons

[0076]

[0077] Borane compounds A through F have the following substituents: AR═R′═R″═F B R′═R″═H; R═Me C R′═R″═H; R═Butyl D R′═R″═H; R═OMe E R′═R″═H;R═CF₃ F R═R″═H; R′═CF₃

General Method of Formation for Anionic Borate Ligands

[0078] Step 1 (R′)₂BQ+R²XCH₂Z′→[(R′)₂B(CH₂YR″)₂] [Z′]

[0079] where:

[0080] R′ is alkyl or aryl. Each R′ may be the same or different. Thearyl can be substituted such as p-MeOPh, p-MePh, p-t-BuPh.

[0081] Q is a halide, triflate, acetate or other labile leaving group.

[0082] Y is P or N;

[0083] R″ is alkyl or aryl. Each R″ may be the same or different.Examples include Ph and t-Bu.

[0084] Z′ is an alkali metal cation such as Li, Na, K or MgQ.

[0085] E is an alkali metal cation of the formula R₄N⁺.

[0086] L is a mono or bidentate, displaceable neutral donor ligand

[0087] Z is a metal. Examples include Ni, Pd and Pt.

[0088] R′″ is halo, pseudo-halo, alkyl or aryl. Each R′″ may be the sameor different.

[0089] Illustrated graphically, the resulting anionic borate ligandproduct from Step 3, has the formula:

EXAMPLE 1 Synthesis of [Ph₂B(CH₂Ph₂)₂][ASN] (1)

[0090] Synthesis of (1) was readily achieved by low-temperature additionof a toluene solution of diphenylchloroborane to a Et₂O solution ofPh₂PCH₂Li(TMEDA). This generates [Ph₂B(CH₂PPh₂)₂][Li(TMEDA)₂], whosestructure is shown below. Cation exchange provided the ASN salt (1) inhigh yield. Details of the synthesis are as follows.

[0091] Solid yellow Ph₂PCH₂Li(TMEDA) (4.82 g, 15.0 mmol) was dissolvedin Et₂O (180 mL)in a Schlenk flask with a stir bar and sealed with aseptum. The reaction vessel was cooled to −78° C. in a dry ice/acetonebath. Ph₂BCl (1.514 g, 7.553 mmol), dissolved in toluene (10 mL),wasintroduced dropwise via syringe to the cooled reaction flask. Thereaction was stirred and warmed gradually to RT over 14 h, providing apale yellow precipitate. Volatiles were removed in vacuo, and theresulting solids were isolated in a drybox on a sintered glass frit andwashed with Et₂O (5×10 mL). Drying in vacuo provided pale yellow solid[Ph₂B(CH₂PPh₂)₂][Li(TMEDA)₂] (5.67 g). Crystals suitable for an X-raydiffraction experiment were grown by slowly cooling a hot toluenesolution of [Ph₂B(CH₂PPh₂)₂][Li(TMEDA)₂]. Solid[Ph₂B(CH₂PPh₂)₂][Li(TMEDA)₂] was dissolved in EtOH (40 mL).

[0092] [Ph₂B(CH₂PPh₂)₂][Li(TMBDA)₂]: (C₅₀H₆₅BLiN₄P₂), MW=801.75,colorless prism, collection temperature=98° K, monoclinic, spacegroup=P2₁/c, a=11.7922(6) Å, b=11.7081(6) Å, c=33.1336(18) Å, α=90°,β=94.0620(10)°, γ=90°, V=4563.1(4) Å³, Z=4, R₁=0.061 [I>2σ(I)],GOF=1.952.

[0093] ASNBr (1.8 g, 8.7 mmol)was dissolved in EtOH (8 mL)and added tostirring (1). A white precipitate formed immediately. The mixture wasstirred for 10 min, and white solids were subsequently collected byfiltration. The solids were washed with EtOH (2×10 mL) and Et₂O (3×10mL) and dried in vacuo for 24 h, providing (1) as a pure, white solid(4.30 g, 6.23 mmol, 83.1%).

[0094]¹H NMR (300 MHz, d₆-acetone): δ=7.29 (b, 4H, ortho B(C₆ H ₅)₂),δ=7.17 (m, 8H, ortho P(C₆H₅)₂), δ=7.00 (m, 12H, meta B(C₆ H ₅)₂ and P(C₆H ₅)₂), δ=6.74 (m, 4H, para P(C₆H₅)₂), δ=6.62 (m, 2H, para B(C₆ H ₅)₂),δ=3.65 (m, 8H, ((CH₂CH ₂)₂)₂N), δ=2.23 (m, 8H, ((CH ₂CH₂)₂)₂N), δ=1.64(b, 4H, Ph₂B(CH ₂PPh₂)₂). ¹³C {¹H} NMR (125.7 MHz, d₆-acetone): δ=165(b, ipso B(C₆H₅)₂), δ=147.4 (d, ipso P(C₆H₅)₂, ¹J_(P-C)=22 Hz), δ=134.7(s, ortho B(C₆H₅)₂), δ=133.6 (d, ortho P(C₆H₅)₂, ²J_(P-C)=19 Hz),δ=127.1 (s, meta P(C₆H₅)₂, ³J_(P-C)=6 Hz), δ=126.0 (s, para P(C₆H₅)₂),δ=125.3 (s, meta B(C₆H₅)₂), δ=121.5 (s, para B(C₆H₅)₂), δ=63.1(((CH₂CH₂)₂)₂N), δ=25.7 (b, [Ph₂B(CH₂PPh₂)₂]), δ=22.1 (((CH₂CH₂)₂)₂N).³¹P {¹H} NMR (121.4 MHz, d₆-acetone): δ=−8.78 (²J_(P-B)=10.0 Hz). ¹¹B{¹H} NMR (128.3 MHz, d₆-acetone): δ=−12.6. Anal. Calcd. for C₄₆H₅₀BNP₂:C, 80.11; H, 7.31; N, 2.03. Found: C, 79.89; H, 7.45; N, 2.15.

EXAMPLE 2 Synthesis of [{Ph₂B (CH₂PPh₂)₂}Pt(Me)₂][ASN] (2) and[{Ph₂B(CH₂PPh₂)₂}Pt(Me)(Ph)][ASN] (3)

[0095] Reaction of (1) with either (COD)Pt(Me)₂ or (COD)Pt(Me)(Ph) inTHF forms the anionic platinum(II) precursors[{Ph₂B(CH₂PPh₂)₂}Pt(Me)₂][ASN] (2) and [{Ph₂B(CH₂PPh₂)₂}Pt(Me)(Ph)][ASN] (3) in high yield. Details of the synthesis are as follows.

[Ph₂B(CH₂PPh₂)₂Pt(CH₃)₂][ASN] (2)

[0096] Solid (1) (391.8 mg, 0.5680 mmol)was suspended in THF (6 mL). Asolution of (COD)Pt(Me)₂ (189.3 mg, 0.5679 mmol) in THF (2 mL) was addedto the suspension, and the reaction homogenized as it stirred. A whiteprecipitate formed after 1 h. The resulting mixture was concentrated invacuo and triturated with pentane (2×2 mL). The off white solids weredried in vacuo, providing (2) as an off-white solid (511.2 mg,98.4%).Crystals suitable for X-ray diffraction were grown from slow evaporationof an acetonitrile solution of (2).

[0097]¹H NMR (300 MHz, d₆-acetone): δ=7.40 (m, 8H, P(C₆H₅)₂), δ=7.07 (m,12H, B(C₆H₅)₂, (P(C₆H₅)₂)₂), δ=6.88 (m, 4H, B(C₆H₅)₂), δ=6.64 (m, 4H,para-(P(C₆H₅)₂)₂), δ=6.58 (m, 2H, para-B(C₆H₅)₂), δ=3.71 (m, 8H, ((CH₂CH₂)₂)₂N), δ=2.26 (m, 8H, ((CH ₂CH₂), −1.98 (b, 4H, Ph₂B(CH ₂PPh₂), −0.08(t, 6H, Pt(CH ₃) ³J_(P-H)=12 Hz, ²J_(Pt-H)=68 Hz). ¹³C {¹H} NMR (125.7MHz, d₆-acetone): δ=167 (b, ipso B(C₆H₅)₂), δ=140.1 (d, ipso P(C₆H₅)₂,¹J_(P-C)=39.0 Hz), δ=134.4 (m, ortho P(C₆H₅)₂), δ=133.5 (s, orthoB(C₆H₅)₂), δ=128.2 (s, meta B(C₆H₅)₂), δ127.3 (m, meta P(C₆H₅)₂),δ=126.3 (m, para P(C₆H₅)₂), δ=122.0 (s, para B(C₆H₅)₂), δ=63.7 (((CH₂CH₂)₂)₂N), δ=22.9 (b, [Ph₂B(CH₂PPh₂)₂]), δ=22.8 (((CH₂CH₂)₂)₂N), δ=5.5(dd, Pt(CH₃)₂, ¹J_(Pt-C)=600 Hz, ²J_(P-C)=103 Hz, ²J_(P-C)=9.1 Hz). ³¹P{H} NMR (121.4 MHz, d₆-acetone): δ=20.60 (¹J_(Pt-P)=1892 Hz). ¹¹B {¹H}NMR (128.3 MHz, d₆-acetone): δ=−13.7. Anal. Calcd. for C₄₈H₅₆BNP₂Pt: C,63.02; H, 6.17; N, 1.53 . Found: C, 62.97; H, 5.90; N, 1.81.

[Ph₂B(CH₂PPh₂)₂Pt(CH₃)(C₆H₅)][ASN] (3)

[0098] A THF solution (1 mL) of (COD)Pt(Me)(Ph)(70.6 mg,0.179 mmol) wasadded to a stirring suspension of (1) (123.1 mg, 0.1785 mmol)in THF (2mL). The reaction was stirred for 30 min and became homogeneous. Thesolution was concentrated in vacuo, and off-white solids wereprecipitated with Et₂O (2 mL). The supernatent was removed, and thesolids were washed with EtOH (2×2mL) and Et₂O (2×2 mL) and dried invacuo, producing off-white (3) (122.4 mg, 70.2%).

[0099]¹H NMR (300 MHz, d₆-acetone): δ=7.47 (m, 4H), δ=7.24 (m, 4H),δ=7.12 (m, 2H), δ=7.09 (m, 4H), δ=6.98 (m, 4H), δ=6.87 (m, 8H), δ=6.62(m, 4H), δ=6.57 (m, 2H), δ=6.43 (m, 2H), δ=6.29 (m, 1H, para Pt-C₆H₅),δ=3.69 (m, 8H, ((CH₂CH ₂)₂)₂)2N), δ2.26 (m, 8H, ((CH₂CH ₂)₂)₂N), δ=2.10(b, Ph₂B(CH ₂PPh₂)₂), δ=2.02 (b, Ph₂B(CH ₂PPh₂)₂), δ=0.08 (dd, 3H, Pt(CH₃), ³J_(P-H) (cis)=6.9 Hz, ³J_(P-H) (trans)=7.8 Hz, ²J_(Pt-H)=69 Hz).¹³C {¹H} NMR (125.7 MHz, d₆-acetone): δ=166 (b, ipso B(C₆H₅)₂), δ=144(b, ipso Pt(C₆H₅)), δ=140.5 (d, ipso P(C₆H₅)₂, ¹J_(P-C)=39.5 Hz),δ=139.8 (d, ipso P(C₆H₅)₂, ¹J_(P-C)=22.5 Hz), δ=138.7 (s, ortho Pt(C₆H₅)¹J_(Pt-C)=32 Hz), δ=135.0 (m, ortho P(C₆H₅)₂), δ=134.7 (m, orthoP(C₆H₅)₂), δ133.8 (s, ortho B(C₆H₅)₂), δ=128.9 (s, meta P(C₆H₅)₂),δ=128.4 (s, meta P(C₆H₅)₂), δ=127.9 (d, para P(C₆H₅)₂, ⁴J_(P-C)=8.5 Hz),δ=127.5 (d, para P(C₆H₅)₂, ⁴J_(P-C)=8.5 Hz), δ=127.0 (s, meta Pt(C₆H₅)),δ=126.8 (s, meta B(C₆H₅)₂), δ=122.4 (s, para B(C₆H₅)₂), δ=120.0 (s, paraPt(C₆H₅)), δ=64.3 (((CH₂ CH₂)₂)₂N), δ=23.3 (((CH₂CH₂)₂)₂N), δ=23 (b,[Ph2B(CH₂PPh₂)₂]), δ=22 (b, [Ph₂B(CH₂PPh₂)₂]), δ=5.5 (dd, Pt-CH₃,²J_(P-C)(trans)=93 Hz). ³¹P {¹H} NMR (121.4 MHz, d₆-acetone): δ=18.3 (d,¹J_(Pt-P)=1775 Hz, ²J_(P-P)=19 Hz), δ=17.29 (d, ¹J_(Pt-P)=1868 Hz,²J_(P-P)=19 Hz). ¹¹B {¹H} NMR (128.3 MHz, d₆-acetone): δ=−13.8. Anal.Calcd. for C₅₃H₅₇BNP₂Pt: C, 65.16; H, 5.98; N, 1.43. Found: C, 64.90; H,6.05; N, 1.54.

EXAMPLE 3 Synthesis of Ph₂B(CH₂PPh₂)₂Pt(CH₃)(THF) (4)

[0100] To generate the key neutral platinum complex,{Ph₂B(CH₂PPh₂)₂}Pt(Me)(L), several strategies were surveyed includingprotonolysis by acid and methide abstraction by B(C₆F₅)₃. All of thesestrategies effected the removal of one methyl group from (2), asdetermined by ³¹P NMR spectroscopy; however, most routes did not enablethe clean isolation of a {Ph₂B(CH₂PPh₂)₂}Pt(Me)(L) complex. It wasdiscovered that protonation of (2) in THF with the bulky ammonium salt[¹Pr₂EtNH][BPh₄] did enable both the clean generation of{Ph₂B(CH₂PPh₂)₂}Pt(Me)(THF) (4) and its isolation. The salt byproduct,[ASN][BPh₄], precipitated from THF and was readily removed. Solid (4)can be subsequently isolated by rapid precipitation from THF withpentane, a procedure that also removes the neutral amine byproduct,¹Pr₂EtN. It is noteworthy that the protonation of (2) directly contrastswith the reactivity of a related compound, (dppp)PtMe₂, which did notexhibit reactivity with [¹Pr₂EtNH][BPh₄] at 50° C. in THF solution over24 h. Details of the synthesis are as follows.

[0101] Solid (2) (49.3 mg, 53.9 tmol)was dissolved in THF (2 mL). A THFsolution (1 mL) of [¹Pr₂EtNH][BPh₄] (24.3 mg, 54.1 μmol)was added to thestirring solution of (2). The clear, colorless reaction rapidly produceda white precipitate. The mixture was stirred for 15 min, and the whitesolids (ASNBPh₄) were filtered away. The solution was concentrated invacuo, and pentane (2 mL)was added, precipitating solid (4) as aspectroscopically pure solid. The solid was collected by filtration. Dueto the lability of the coordinated THF molecule, obtaining satisfactorycombustion analysis was problematic.

[0102]¹H NMR (300 MHz, C₆D₆): δ=7.64 (m, 4H, aryl protons), δ=7.48 (m,4H, aryl protons), δ=7.24 (m, 4H, aryl protons), δ=7.00 (m, 18H, arylprotons), δ=2.90 (b, 4H, Pt—O(CH ₂CH₂)₂), δ=2.51 (d, 2H, Ph₂B(CH₂PPh₂)₂, ²J_(P-H)=18 Hz), δ2.37 (d, 2H, Ph₂B(CH ₂PPh₂)₂, ²J_(P-H)=14Hz), δ=0.71 (b, 4H, Pt—O(CH₂CH ₂)₂), δ=0.35 (bd, 3H, Pt-CH ₃, ³J_(P-H)=6Hz, ²JP_(t-H)=40 Hz). ¹³C {¹H} NMR (125.7 MHz, THF, −5° C.): δ=160.3 (b,ipso B(C₆H₅)₂), δ134.1 (d, ispo P(C₆H₅)₂, ¹J_(P-C)=42.1 Hz), δ=130.9 (d,ortho P(C₆H₅)₂, ²J_(P-C)=11.2 Hz), δ=130.8 (d, ortho P(C₆H₅)₂,²J_(P-C)=10.7 Hz), δ=130.1 (d, ipso P(C₆H₅)₂, ¹J_(P-C)=32.6 Hz), δ=129.7(s, ortho B(C₆H₅)₂), δ=127.3 (s, meta P(C₆H₅)₂), δ=126.9 (s, metaP(C₆H₅)₂), δ=125.5 (d, para P(C₆H₅)₂, ⁴J_(P-C)=9.1 Hz), δ=125.1 (d, paraP(C₆H₅)₂, ⁴J_(P-C)=11.2 Hz), δ=123.5 (s, meta B(C₆H₅)₂), δ=119.2 (s,para

[0103] B(C₆H₅)₂), δ=64.9 (Pt—O(CH₂CH₂)₂), δ=22.6 (Pt—O(CH₂CH₂)₂), δ=21.2(b, [Ph₂B(CH₂PPh₂)₂]), δ=15.3 (b, [Ph₂B(CH₂PPh₂)2]), δ=8.2 (dd, Pt-CH₃,²J_(P-C)(trans) −85.5 Hz, ²J_(P-C) (cis) −4.8 Hz). ³¹P {¹H} NMR (121.4MHz, THF): δ=33.44 (¹J_(Pt-P)=1820 Hz, ²J_(P-P)=22 Hz), δ=15.96(¹J_(Pt-P)=4478 Hz, ²J_(P-P)=22 Hz). ¹¹B {¹H} NMR (128.3 MHz, THF):δ=−14.5.

[0104] An X-ray diffraction study on single crystals of (4) confirmedits structural assignment: (4)-2(THF) (C₄₃H₄₅BOP₂Pt.2(C₄H₈₀)),MW=845.67×2(72.10), colorless block, collection temperature=98° K,triclinic, space group=P, a=12.210(4) Å, b=12.803(4) Å, c=16.205(5) Å,α=109.614(5)°, β=104.361(5)°, γ=96.489(5)°, V=2257.6(12) Å³, Z=2,R₁=0.043 [I>2σ(I)], GOF=1.404.

[0105] To date, this represents the third crystallographicallycharacterized example of a platinum-THF adduct and is the only chargeneutral species thus characterized for divalent platinum (Butts et al,J. Am. Chem. Soc. 118:11831-11843 (1996); Schlect et al., Angew. Chem.,Int. Ed. Engl. 36:1994-1995 (1997)). Importantly, the coordinated THFmolecule in (4) is weakly bound: it is readily substituted by a varietyof neutral ligands (CO, pyridine, H₂O, acetone, Et₃N) and is veryunstable under reduced pressure (placing (4) under vacuum leads to asingle new product whose identity has yet to be determined). It shouldalso be noted that (4) slowly degrades in THF solution at ambienttemperature.

EXAMPLE 4 Generation of Ph₂B(CH₂PPh₂)₂Pt(C₆H)(THF) (5)

[0106] The ability of complex (4) to engage the aryl C—H bonds ofbenzene was examined. When a solid sample of (4) was dissolved andgently warmed in benzene, a solvent in which it is appreciably soluble,formation of one major product was observed. At 50° C., the reaction wascomplete after 4 h. The major product (80%) formed was{Ph₂B(CH₂PPh₂)₂}Pt(Ph)(THF) (5) based upon spectroscopic data. Toconfirm its assignment, (5) was independently generated by methideabstraction from (3) with B(Ar)₃ in THF. It is noted that addition ofseveral molar equivalents of THF to a benzene solution of (4) slows therate of benzene activation. The conversion of (4) to (5) occurs ingreater yield in the presence of several molar equivalents of THF,albeit more slowly. Notably, H₂O has been observed to inhibit C—Hactivation in related systems by Tilset and co-workers (Heiberg et al.,J. Am. Chem. Soc. 122:10831-10845 (2000)). Details of the reaction areas follows.

[0107] Solid (3) (23.6 mg, 24.2 [tmol)was dissolved in THF (2 mL). SolidB(C₆F₅)₃ (12.5 mg,24.4 μmol) was added to the stirring solution of (3).After 10 min, ³¹P NMR analysis showed the formation of one majorproduct, consistent with the formulation of (5).

[0108] Solid (3) (51.4 mg, 52.6 μmol) was dissolved in THF (2 mL). A THFsolution (2 mL)of [^(i) Pr₂EtNH][BPh₄] (23.5 mg, 52.3 μmol)was added tothe stirring solution of (3). The clear, colorless reaction slowlyproduced a white precipitate. The mixture was stirred for 1 h, and thewhite solids were filtered away. The solution was concentrated in vacuo,and pentane (2 mL) was added, precipitating white solids. The solidswere collected by filtration. NMR analysis of the solids was consistentwith the formulation of (5) as the major product (˜80%). Due to thelability of the coordinated THF molecule, obtaining satisfactorycombustion analysis was problematic.

[0109]¹H NMR (300 MHz, C₆D₆): δ=7.56 (m, 4H, aryl protons), δ=7.46 (m,4H, aryl protons), δ=7.21 (m, 4H, aryl protons), δ=6.95 (m, 18H, arylprotons), δ=6.88 (m, 2H, Pt(C₆H₅)), δ=6.78 (m, 2H, Pt-C₆H₅), δ=6.73 (m,1H, para Pt-C₆H₅), δ=2.87 (b, 4H,Pt—O(CH₂CH₂)₂), δ=2.64 (d, 2H,Ph₂B(CH₂PPh₂)₂, ²J_(P-H=)17 Hz), δ=2.42 (d, 2H, Ph₂B(CH₂PPh₂)₂,²J_(P-H)=14 Hz), δ=0.46 (b, 4H, Pt—O(CH₂CH₂)₂). ¹³C {¹H} NMR (125.7 MHz,THF): δ=161 (b, ipso B(C₆H₅)₂), δ=136.3 (s, ortho Pt(C₆H₅)), δ=135.4 (d,ipso P(C₆H₅)₂, ¹J_(P-C)=43.8 Hz), δ=133.0 (d, ortho P(C₆H₅)₂,²J_(P-C)=10.7 Hz), δ=132.9 (d, ortho P(C₆H5) ²J^(P-C)=11.2 Hz), δ=132.1(d, ipso P(C₆H₅) ¹J_(P-C)=57.7 Hz), δ=131.5 (s, ortho B(C₆H₅), δ=129.2(s, meta P((C₆H₅)₂), δ=129.1 (s, meta P(C₆H₅)₂), δ=127.6 (d, paraP(C₆H₅)₂, ⁴J_(P-C)=9.1 Hz), δ=126.9 (d, para P(C₆H₅)₂, ⁴J_(P-C)=11.2Hz), δ=126.4 (d, meta Pt(C₆H₅), ⁴J_(P-C)=9.6 Hz), δ=125.5 (s, metaB(C₆H₅)₂), δ=122.6 (s, para Pt(C₆H₅)), δ=121.2 (s, para B(C₆H₅)₂), δ=67(Pt—O(CH₂CH₂)₂), δ=26 (Pt—O(CH₂CH₂)₂), δ=21 (b,[Ph₂B(CH₂PPh₂)₂]), δ=17(b, [Ph₂B(CH₂PPh₂)₂]). ³¹P {¹H} NMR (121.4 MHZ, THF). δ=28.60(¹J_(Pt-P)=1740 Hz, ²J_(P-P)=23 Hz), δ=11.20 (¹J_(Pt-P)=4393 Hz,²J_(P-P)=23 Hz). ¹¹B {¹H} NMR (128.3 MHz, THF): δ=−14.9.

Reaction of (4) With Benzene

[0110] Solid 4 was generated as above and dissolved in benzene (2 mL).The solution was concentrated in vacuo (vol≈0.5 mL). Benzene was added(1 mL), and the solution was again concentrated in vacuo (vol≈0.7 mL).Concentration of the benzene solution serves to ensure complete removalof residual pentane. The solution was placed in an NMR tube, and aninitial ³¹P NMR spectrum showed the presence of one species (4). The NMRtube was heated to 50° C. and monitored by ³¹P NMR spectroscopy. After 4h, ³¹P NMR spectroscopy showed the presence of 4 products, where (5) wasthe major product (ca.80%). The identities of the three minor byproductshave yet to be confirmed. They may result from (i)ligand activation,(ii)THF activation, or (iii) bimolecular reaction pathways.

[0111] Analogous to its reactivity with benzene, (4) was found to reactwith toluene preferentially at the C—H bonds of the aryl ring. There isno evidence for competitive benzylic C—H activation. Spectroscopicevidence suggests that the predominant isomer formed is the p-tolylplatinum complex and we the product ratio of 3:1:1 was tentativelyassigned to the para:meta:ortho isomers, respectively.

EXAMPLE 5 Bond Activation Activity of (4)

[0112] Preliminary studies have been conducted to evaluate the potentialof (4) to activate alkyl C—H bonds. As yet, no conclusive observationshave been made as to the occurrence of such a reaction. Incubation of aTHF solution of (4) under an atmosphere of ¹³CH₄ at 75° C. for 10 hafforded no detectable incorporation (¹³C NMR) of an isotopicallyenriched methyl group. This contrasts results reported for complexeswith amine and imine donor ligands, where ¹³CH₄ has been demonstrated toreversibly react with the compounds [(TMEDA)Pt(CH₃)(NC₅F₅)]⁺ inpentafluoropyridine and [(ArNdC—CdNAr)Pt(CH₃)(H₂O)]⁺ in DCM.Additionally, no reaction occurred upon dissolution of (4) in a 1:1THF:cyclohexane mixture at 75° C. over a period of 12 h. A possiblereaction between (4) and the C—H bonds of methane or cyclohexane islikely inhibited by the presence of a large excess of tetrahydrofuran.Complex (4), while soluble in aromatic hydrocarbons, reacts rapidly withthem relative to other, nonaromatic solvent molecules; however, (4) isnot appreciably soluble in simpler hydrocarbons such as pentane andcyclohexane, and hence its reactivity in the absence of solubilizing THFequivalents has yet to be determined.

EXAMPLE 6 Synthesis of (CH₃)₂N(BH₃)CH₂Li.(THF) (6)

[0113] The room temperature addition of n-BuLi to a THF solution ofMe₃N.BH₃ cleanly affords (CH₃)₂N(BH₃)CH₂Li(THF) (6) as a white,microcrystalline solid. Details of the reaction are as follows.

[0114] A solution of 1.6 M n-BuLi in hexanes (85.7 ml, 0.137 mol) wasadded portion-wise to a stirring solution of H₃B.NMe₃ (10 g, 0.137 mol)dissolved in THF (20 mL) under a dinitrogen atmosphere. Addition wascomplete after 5 min. Concentration of the reaction solution to 50 mLafter stirring for 5h resulted in precipitation of (6). The reactionsolution was decanted from the product, which was washed with petroleumether (3×40 mL), and dried in vacuo affording spectroscopically pure(6), (9.2 g, 44%). The mother liquor was further concentrated to yield asecond crop of (6) (3.2 g). The total isolated yield was 12.4 g (60 %).

[0115]¹H NMR (C₆D₆, 300 MHz, 25° C.): δ3.55 (m, 4H, (CH₂CH ₂)₂O—Li),2.68 (s, 6H, (Li—CH₂N(CH ₃)₂)), 2.01 (bs, 2H, (Li—CH ₂N(CH₃)₂)), 1.30(m, 4H, (CH ₂CH₂)₂O—Li). ¹³C NMR (C₆D₆, 75.409 MHz, 25° C.): δ69(Li—CH₂N(CH₃)₂, 67 ((CH₂CH₂)₂O—Li), 60.2 (Li—CH₂N(CH₃)₂), 26((CH₂CH₂)₂O—Li). ¹¹B{¹H} NMR (C₆D_(6,) 128.3 MHz, 25° C.): δ−10.16

EXAMPLE 7 Synthesis of [Ph₂B(CH₂N(BH₃)(CH₃)₂)₂][Li(TMEDA)₂] (7)

[0116] Addition of (CH₃)₂N(BH₃)CH₂Li(THF) (6) to half an equivalent ofPh₂BCl (25° C.; toluene) generates the borane-protected amino(borate)complex [Ph₂B(CH₂N(BH₃)Me₂)₂][Li]. This species is convenientlyprecipitated from Et₂O by addition of TMEDA to produce[Ph₂B(CH₂N(BH₃)Me₂)₂][Li(TMEDA)₂] (7) as a white solid. Details of thereaction follows.

[0117] A solution of Ph₂BCl (268 mg, 1.3 mmol) in toluene (5 mL) wasadded dropwise to (CH₃)₂N(BH₃)CH₂Li.(THF) (6) (405 mg, 2.6 mmol) intoluene (6 mL). When the addition was complete after 5 min., thesolution became turbid as LiCl precipitated from solution. The reactionwas allowed to stir for 6 hours when the toluene was removed in vacuo.The resulting oily solid was taken up in 5 mL Et₂O and filtered throughCelite to remove the LiCl salts. Upon the addition of TMEDA (350 mg, 3mmol), (7) precipitated from the ether solution. (7) was isolated viafiltration and washed with petroleum ether (3×10 mL), and dried in vacuoaffording spectroscopically pure (7), (510 mg, 69%). Crystals were grownvia petroleum ether diffusion into a benzene solution.

[0118]¹H NMR (C₆D₆, 300 MHz, 25° C.): δ8.18 (d, J=7.2 Hz, 4H, ortho B(C₆H ₅)₂), 7.44 (t, J=7.2 Hz, 4H, meta B(C₆ H ₅)₂), 7.26 (t, J=7.2 Hz, 2H,para B(C₆ H ₅)₂), 3.27 (b, 4H, Ph₂B(CH ₂N(BH₃)(CH₃)₂), 2.33 (s, 12H,Ph₂B(CH₂N(BH₃)(CH ₃)₂)), 1.954 (s, 34H, TMEDA-Li). ¹³C NMR (C₆D₆, 75.409MHz, 25° C.): δ162 (b, ipso (B(C ₆H₅)₂), 136 (s, ortho (B(C ₆H₅)₂),127.6 (s, meta (B(C ₆H₅)₂), 124.4 (s, para (B(C ₆H₅)₂), 72 (b,Ph₂B(CH₂N(BH₃) (CH₃)₂), 58 (s, (CH₃)₂N(CH₂)₂), 53 (s, (CH₃)₂N(CH₂)₂), 47(s, Ph₂B(CH₂N(BH₃) (CH₃)₂). ¹¹B {¹H} NMR (C₆D₆, 128.3 MHz, 25° C.):δ−7.77 Ph₂B(CH₂N(BH₃)(CH₃)₂), −13.9 Ph₂ B(CH₂N(BH₃)(CH₃)₂). ES−MS(Electrospray): calculated for C₁₈H₃₂B₃N₂ (M)⁻ m/z 309, found (M+H)⁻ m/z309, 295 (M−BH₃). Anal. Calculated for C₃₀H₆₄B₃LiN₆: C, 65.72; H, 11.77;N, 15.33. Found: C, 65.38; H, 11.69, N, 15.08.

EXAMPLE 8 Synthesis of [Ph₂B(CH₂NMe₂)₂][Li] (8)

[0119] To derive the target ligand, numerous methods were evaluated toremove the borane protecting group from [Ph₂B(CH₂N(BH₃)Me₂)₂]⁻. Boraneliberation from alkylamines is traditionally accomplished by transfer toanother strong Lewis base, acidification, or oxidation (Schmidbaur, J.Organomet. Chem. 200:287 (1980); Imamotoet al., J. Am. Chem. Soc.112:5244 (1991); Brunel et al., Coord. Chem. Rev. 665:178-180 (1998);Carboni et al., Tetrahedron 55:1197 (1999); borane protected benzylicamines and substituted aziridines have been alkylated via intermediategeneration of a benzylic or aziridinyl carbanion in Ebden et al,Tetrahedron 1998, 54(42):129 (1998) and Vedejs et al., J. Am. Chem. Soc.119:6941 (1997); and Couturier et al, Organic Lett. 3(3):465 (2001)).Unfortunately, [Ph₂B(CH₂N(BH₃)Me₂)2]⁻ degrades to Me3N.BH₃ on exposureto strong acid (e.g. HCl) and resists borane oxidation in the presenceof Pd/C in methanol (25 wt % Pd/C, 3 days, 25° C.). The focus turned toa Lewis base deprotection strategy. The system of choice proved to be a25-fold excess of DABCO (toluene, 100° C., complete and quantitativeafter 10 h as determined by ¹¹B NMR). The excess DABCO was effectivelyrecovered by sublimation (120° C., 10 torr), and the target ligand[Ph₂BN^(Me) ₂] was isolated as its lithium salt [Ph₂BN^(Me) ₂][Li] (8),in yields typically exceeding 80%. Details of the reaction are asfollows.

[0120] [Ph₂B(CH₂NMe₂(BH₃))₂][Li(TMEDA)₂] (7) (1.0 g, 1.78 mmol) andDABCO (5.0 g, 44.6 mmol) were dissolved in toluene (15 mL). The solutionwas heated to 100° C. for 10 hours. Borane transfer was monitored by ¹¹BNMR. The toluene was removed in vacuo and the unused DABCO reagent wassublimed under static vacuum from the solid mixture at 60° C. TheDABCO.BH₃ complex was sublimed under dynamic vacuum at 125° C. Theremaining white solid was washed with pet ether (2×2 mL) and dried invacuo to yield 442 mg of (8) (86%).

[0121]¹H NMR (acetone-d₆, 300 MHz, 25° C.): δ7.31 (d, J=7.2 Hz, 4H,ortho B(C₆H₅)₂), 6.98 (t, J=7.2 Hz, 4H, meta B(C₆ H ₅)₂), 6.80 (t, J=7.2Hz, 2H, para B(C₆ H ₅)₂), 2.81 (q, ²J_(B-H)=3.6 Hz, 4H, Ph₂B(CH₂N(CH₃)₂), 2.47 (s, 12H, Ph₂B(CH₂N(CH ₃)₂). ¹³C NMR (acetone-d₆, 125.7MHz, 25° C.): δ162.4 (q, ¹J_(B-C)=50.3 Hz, ipso B(C ₆H₅)₂), 132.8 (s,ortho B(C ₆H₅)₂), 127 (s, meta B(C ₆H₅)₂), 123 (s, para B(C ₆H₅)₂), 63.1(q, ¹J_(B-C)=43.4 Hz, Ph₂B(CH₂N(CH₃)₂), 47.7 (s, Ph₂B(CH₂N(CH₃)₂). ¹¹B{¹H} NMR (acetone-d₆, 128.3 MHz, 25° C.): δ−17.8. ES-MS (Electrospray):calculated for C₁₈H₂₆BN₂ (M)⁻ m/z 281, found (M)⁻ m/z 281; (M+2H)⁺ m/z283, found 283.

EXAMPLE 9 Synthesis of [Ph₂B(CH₂NMe₂)₂][NEt₄] (9)

[0122] The ammonium salt [Ph₂BN^(Me) ₂][NEt₄] (9) forms readily uponaddition of an ethanolic solution of Et₄NBr to (3). Details of thereaction are as follows.

[0123] Alternately, KOC(CH₃)₃ (55 mg, 0.5 mmol) in 0.5 mL THF was addeddropwise to

[0124] Ph₂B(CH₂NMe₂)₂][H] (100 mg, 0.25 mmol) in benzene (2 mL).[Ph₂B(CH₂NMe₂)₂][K] precipitated from solution as a white solid. Thesolution was decanted and the solids dried and isolated. The solids werewashed with benzene (3×3 mL) and petroleum ether (3×1.5 mL) and dried invacuo. Solid [Ph₂B(CH₂NMe₂)₂][K] (25 mg, 0.078 mmol) was dissolved inEtOH (1.5 mL) and added to a solution of [NEt₄][Br] (19.7 mg, 0.094mmol) in EtOH (1 mL). Solid KBr precipitates from solution and wasfiltered over a sintered glass frit. The EtOH was removed in vacuoproducing a white solid. The solids were washed with EtOH/petroleumether (1:3, 3 mL) to yield (9) (29.6 mg, 92%).

[0125]¹H NMR (acetone-d₆, 300 MHz, 25° C.): δ7.33 (d, J=7.5 Hz, 4H,ortho B(C₆H₅)₂), 6.92 (t, J =7.5 Hz, 4H, meta B(C₆H₅)₂), 6.73 (t, J=7.5Hz, 2H, para B(C₆H₅)₂), 3.42 (q, J=7.2 Hz, 8H, N(CH ₂CH₃)₄), 2.57 (m,4H, Ph₂B(CH ₂N(CH₃)₂), 2.22 (s, 12H, Ph₂B(CH₂N(CH ₃)₂), 3.42 (tt, J=2.1,7.2 Hz, 12H, N(CH₂CH ₃)₄). ¹³C NMR (acetone-d₆, 125.7 MHz, 25° C.):δ162.4 (q, ¹J_(B-C)=50.3 Hz, ipso B(C ₆H₅)₂), 132.8 (s, ortho B(C₆H₅)₂), 127 (s, meta B(C ₆H₅)₂), 123 (s, para B(C₆H₅)₂), 63.1 (q,¹J_(B-C)=43.4 Hz, Ph₂B(CH₂N(CH₃)₂), 47.7 (s, Ph₂B(CH₂N(CH₃)₂). ¹¹B {¹H}NMR (acetone-d₆, 128.3 MHz, 25° C.): δ−18.0. ES-MS (Electrospray):calculated for C₁₈H₂₆BN₂ (M)⁻ m/z 281, found (M)⁻ m/z 281; (M+2H)⁻ m/z283, found 283.

EXAMPLE 10 Synthesis of [Ph₂B(CH₂N(BH₃)(CH₃)₂)₂][NEt₄] (10)

[0126]

[0127] NEt₄Br (21 mg, 0.1 mmol) in EtOH (0.5 mL) was added to a solutionof [Ph₂B(CH₂N(BH₃)(CH₃)₂)₂][Li(TMEDA)₂] (7) (218 mg, 0.091 mmol) in of(10) grew from the solution. The remaining solution was decanted and thecrystals washed with EtOH (2×1 mL) and pet ether (2×1 mL). The solidswere dried in vacuo to yield 154.7 mg (88.6%).

[0128]¹H NMR (acetone-d₆, 300 MHz, 25° C.): δ7.64 (d, J=7.5 Hz, 4H,ortho B(C₆ H ₅)₂), 7.08 (t, J=7.5 Hz, 4H, meta B(C₆ H ₅)₂), 6.92 (t,J=7.5 Hz, 2H, para B(C₆ H ₅)₂), 3.46 (q, J=7.2 Hz, 8H, N(CH ₂CH₃)₄),2.78 (q, ²J_(B-H)=3.6 Hz, 4H, Ph₂B(CH ₂N(BH₃)(CH₃)₂)), 1.96 (s, 12H,Ph₂B(CH₂N(BH₃)(CH ₃)₂)), 1.38 (tt, J=2.1, 7.2 Hz, 12 H, N(CH₂CH ₃)₄).¹³C NMR (acetone-d₆, 125.7 MHz, 25° C): δ158 (q, ipso B(C ₆H₅)₂), 136(s, ortho B(C ₆H₅)₂), 127 (s, meta B(C ₆H₅)₂), 124 (s, para B(C ₆H₅)₂),69.8 (q, ¹J_(B-C)=43.2 Hz, Ph₂B(CH₂N(CH₃)₂), 47.7 (s,Ph₂B(CH₂B(CH₂N(CH₃)₂). ¹¹B {¹H} NMR (C₆D_(6,) 128.3 MHz, 25° C.): δ−5.1,−14. ES-MS (Electrospray): calculated for C₁₈H₃₂B₃N₂ (M)⁻ m/z 309, found(M+H)⁻ m/z 309, 295 (M-BH₃). Anal. Calculated for C₂₆H₅₂B₃N₃; C, 71.11;H, 11.94; N, 9.57. Found: C, 70.98; H, 11.90; N, 9.38.

EXAMPLE 11 Synthesis of [Ph₂B(CH₂NMe₂)₂][H] (11)

[0129] An attempt to deprotect the ammonium salt[Ph₂B(CH₂N(BH₃)Me₂)₂][NEt₄] (10) resulted in a Hoffmann degradation ofthe ammonium cation and led to the formation of [Ph₂BNMe₂][H] (11). Thefortuitous formation of this free acid derivative provides access to arange of other salts, [Ph₂BN^(Me) ₂][M⁺], by simple base deprotonation(where M⁺=Li, Na, K from ^(n)BuLi, NaO^(t)Bu, and KO^(t)Bu,respectively. Details of the reaction are as follows.

[0130] [Ph₂B(CH₂NMe₂(BH₃))₂][NEt₄] (10) (261 mg, 0.06 mmol) and DABCO(3.33 g, 0.03 mol) were suspended in toluene (5 mL). The solution washeated to 100° C. for 10 hours. Borane transfer was monitored by ¹¹BNMR. The toluene was removed in vacuo and the unused DABCO reagent wassublimed under vacuum from the solid mixture at 60° C. Upon dissolvingthe solids in EtOH, a white precipitate formed. The EtOH was decantedfrom the solid. The solid was washed with petroleum ether (2×2 mL) anddried in vacuo to yield 78 mg of (11) (47%).

[0131]¹H NMR (acetone-d₆, 300 MHz, 25° C.): δ7.31 (d, J=7.2 Hz, 4H,ortho B(C₆H₅)₂), 6.98 (t, J=7.2 Hz, 4H, meta B(C₆ H ₅)₂), 6.80 (t, J=7.2Hz, 2H, para B(C₆ H ₅)₂), 2.81 (q, ²J_(B-H)=3.6 Hz, 4H, Ph₂B(CH₂N(CH₃)₂), 2.47 (s, 12H, Ph₂B(CH₂N(CH ₃)₂). ¹¹B {¹H} NMR(acetone-d_(6.)128.3 MHz, 25° C.): δ−24. ES-MS (Electrospray):calculated for C₁₈H₂₆BN₂ (M)⁻ m/z 281, found (M)⁻ m/z 281; (M+2H)⁺ m/z283, found 283.

EXAMPLE 12 Synthesis of Ph₂B(CH₂NMe₂)₂Rh(NBD) (12)

[0132] The lithium salt [Ph₂BN^(Me) ₂][Li] (8) underwent smoothtransmetallation with [(NBD)RhCl]₂ to afford a yellow, crystallinerhodium complex {Ph₂B(CH₂NMe₂)₂}Rh(NBD) (12). Details of the reactionare as follows.

[0133] A solution of [Ph₂B(CH₂NMe₂)₂][Li] (8) (50.2 mg, 0.174 mmol) inacetone (2 mL) was added to a solution of [(NBD)RhCl]₂ (40.2 mg, 0.173mmol) in benzene (1 mL) at room temperature. After stirring for 2 h, thesolvent was removed in vacuo. The yellow solid was dissolved in benzeneand filtered through a Celite plug to yield a yellow solution. Thebenzene was removed in vacuo, then the solids were washed with petroleumether (3×1.5 mL). The solids were dried in vacuo to yield 71.4 mg (86%)of (12).

[0134]¹H NMR (C₆D₆, 300 MHz, 25° C.): δ7.66 (m, 4H, ortho B(C₆ H ₅)₂),7.37 (t, J=7.2 Hz, 4H, meta B(C₆ H ₅)₂), 7.15 (t, J=7.2 Hz, 2H, paraB(C₆ H ₅)₂), 3.089 (b, 2H, NBD), 2.91 (dd, J=2.1, 5.1 Hz, 4H, NBD), 2.62(q, ²J_(B-H)=3.6 Hz, 4H, Ph₂B(CH ₂N(CH₃)₂), 1.66 (s, 12H, Ph₂B(CH₂N(CH₃)₂), 0.84 (b, 2H, NBD). ¹³C NMR (C₆D₆, 125.7 MHz, 25° C.): δ165 (m,ipso B(C ₆H₅)₂), 132.6 (s, ortho B(C ₆H₅)₂), 127.6 (s, meta B(C ₆H₅)₂),123.5 (s, para B(C ₆H₅)₂), 65.2 (q, ¹J_(B-C)=44.3 Hz, Ph₂B(CH₂N(CH₃)₂),62.7 (NBD), 57.7 (d, ¹J_(Rh-C)=10 Hz, NBD), 52.7 (s, Ph₂B(CH₂N(CH₃)₂),50.1 (NBD). ¹¹B {¹H} NMR (acetone-d₆, 128.3 MHz, 25° C.): δ−17.5 EM-MS(Electrospray): calculated for C₂₅H₃₄BN₂Rh (M)⁻ m/z 476, found (M)⁺ m/z476. Anal. Calculated for C₂₅H₃₄BN₂Rh: C, 63.05; H, 7.20; N, 5.88.Found: C, 62.85; H, 7.18; N, 5.53.

EXAMPLE 13 Synthesis of Ph₂B(CH₂NMe₂)₂Rh(NCCH₃)₂ (13)

[0135] Hydrogenation of (12) in acetonitrile afforded the well-behavedcatalyst precursor {Ph₂BN^(Me) ₂}Rh(NCCH₃)₂ (13). Details of thereaction are as follows.

[0136] A solution of Ph₂B(CH₂NMe₂)₂Rh(NBD) (12) (25 mg, 0.054 mmol) inTHF/acetonitrile (1:1, 1.5 mL) was charged to a Fisher-Porter bottleunder 40 psi of hydrogen. After stirring vigorously for 1 hr, yellowprecipitate was apparent. The remaining solvent was removed in vacuo toproduce a yellow solid (13). The solids were washed with petroleum etherand dried in vacuo (23 mg, 92%).

[0137]¹H NMR (C₆D₆, 300 MHz, 25° C.): δ7.67 (m, 4H, ortho B(C₆ H ₅)₂),7.39 (t, J=7.2 Hz, 4H, meta B(C₆ H ₅)₂), 7.16 (t, J=7.2 Hz, 2H, paraB(C₆ H ₅)₂), 2.70 (q, ²J_(B-H)=3.6 Hz, 4H, Ph₂B(CH₂N(CH₃)₂), 1.71 (s,12H, Ph₂B(CH₂N(CH ₃)₂), 1.37 (s, 6H, (NCCH ₃)). ¹³C NMR (C₆D₆, 125.7MHz, 25° C.): δ165 (m, ipso B(C ₆H₅)₂), 132.6 (s, ortho B(C ₆H₅)₂),127.6 (s, meta B(C ₆H₅)₂), 123.5 (s, para B(C ₆H₅)₂), 65.2 (q,¹J_(B-C)=44.3 Hz, Ph₂B(CH₂N(CH₃)₂), 52.7 (s, Ph₂B(CH₂N(CH₃)₂). ¹¹B {¹H}NMR (C₆D₆, 128.3 MHz, 25° C.): δ−17.5. ES—MS (Electrospray): calculatedfor C₂₅H₃₄BN₂Rh (M)⁻ m/z 466, found (M)⁺ m/z 425 (M-NCCH₃), 304(M-2NCCH₃).

EXAMPLE 14 Synthesis of Ph₂B(CH₂NMe₂)₂Rh(CO)₂ (14)

[0138] Notably, acetonitrile adducts of more typical, cationic rhodiumprecursors, [L₂Rh(NCCH₃)₂]⁺, typically show poor catalytic activitybecause acetonitrile binds the cationic center too tightly. It istheorized that the zwitterionic {Ph₂BNMe₂}Rh(NCCH₃)₂ complex is a goodpre-catalyst due to its attenuated electrophilicity by comparison totraditional, truly cationic systems. To qualitatively examine thevalidity of this argument, {Ph₂B(CH₂NMe₂)₂}Rh(CO)₂ (14) was prepared andits i)(CO) stretching vibrations compared with the cationic, structuralanalog [(TMEDA)Rh(CO)₂][ClO₄] (Uson et al., J. Organomet. Chem.105(3):365 (1976)). The zwitterionic (14) was found to be more electronrich ((14), υ(CO)(CH₂Cl₂): 2069, 1992 cm⁻¹; [(TMEDA)Rh(CO)₂][ClO₄] υ(CO)(CH₂Cl₂): 2080, 2010 cm⁻¹. Details of the reaction are as follows.

[0139] Alternately, a solution of [(CO)₂RhCl]₂ (5 mg, 0.013 mmol) in THF(0.5 mL) was added to a stirring solution of [Ph₂B(CH₂NMe₂)₂][NEt₄] (9)(10.6 mg, 0.013 mmol in THF (1 mL) at room temperature. After stirringfor 5 minutes, the solution was filtered through a Celite plug and thenthe THF was removed in vacuo to yield (14).

[0140]¹H NMR (C₆D₆, 300 MHz, 25° C.): δ7.66 (m, 4H, ortho B(C₆H₅)₂),7.37 (t, J=7.2 Hz, 4H, meta B(C₆H₅)₂), 7.15 (t, J=7.2 Hz, 2H, para B(C₆H ₅)₂), 2.66 (q, ²J_(B-H)=3.6 Hz, 4H, Ph₂B(CH ₂N(CH₃)₂), 1.73 (s, 12H,Ph₂B(CH₂N(CH₃)₂). ¹³C NMR (C₆D₆, 125.7 MHz, 25° C.): δ165 (m, ipso B(C₆H₅)₂), 132.6 (s, ortho B(C ₆H₅)₂), 127.6 (s, meta B(C ₆H₅)₂), 123.5 (s,para B(C ₆H₅)₂), 65.2 (q, ¹J_(B-C)=44.3 Hz, Ph₂B(CH₂N(CH₃)₂), 52.7 (s,Ph₂B(CH₂N(CH₃)₂). ¹¹B {¹H} NMR (C₆D₆, 128.3 MHz, 25° C.): δ−17.3. IR:(CH₂Cl₂) ν_(CO)=2069.6, 1992 cm⁻¹.

EXAMPLE 15 Catalysis Reactions with (13)

[0141] It is well known that cationic rhodium(I) precursors supported byneutral, bidentate ligands can be excellent catalysts for organometallictransformations. These processes include catalytic hydrogenation(Schrock et al., J. Am. Chem. Soc. 93:3091 (1971); Crabtree, Acc. Chem.Res. 12:331 (1979); and Crabtree, Homogeneous Catalysis (Ch. 9). TheOrganometallic Chemistry of the Transition Metals. 3^(rd) Edition; JohnWiley & Sons: New York, N.Y., 206-236 (2001)), hydrosilation (Ojima, TheChemistry of Organic Silicon Compounds; Patai, S.; Rappoport, Z., Eds.;Wiley: New York, 1989; Chapter 25), hydroboration (Burgess et al., Chem.Rev. 91:1179 (1991); and Evans et al., J. Am. Chem. Soc. 110:6917(1988)), hydroamination (Burling et al., Organometallics 19:87 (2000);and Hartung et al., J. Org. Chem. 66:6339 (2001)), and hydroacylationreactions (Bosnich, Acc. Chem. Res. 31:667 (1998)). The mediation ofrelated transformations by the neutral, but formally zwitterionic“{Ph₂BN^(Me) ₂} Rh⁺” precursors was evaluated. Details of the reactionare as follows.

[0142] Styrene (44.5 mg, 0.43 mmol) and catecholborane (46 mg, 0.38mmol) were added to a THF (1 mL) solution of (13) (1 mg, 2 μmol). Thereaction was monitored by ¹¹B NMR and borane transfer was judgedcomplete at 1.5 h. GC/MS analysis showed the product peaks at m/z=224,104. Compound (13) was shown to be an active catalyst for thishydroboration reaction (93% GC/MS, 0.5 mol % of (13), 1.5 h)

[0143] Styrene (44.5 mg, 0.43 mmol) and diphenylsilane (70 mg, 0.38mmol) were added to a C₆D₆ (0.7 mL) solution of (13) (1 mg, 2 μmol). Thereaction was monitored by ¹H NMR and silane transfer was judged completeat 1 h. GC/MS analysis showed the product peaks at m/z=288, 104.Compound (13) was shown to be an active catalyst for this hydrosilationreaction (96% GC/MS, 0.5 mol % of (13), 1 h)

[0144] 4-methyl-4-pentenal (42 mg, 0.43 mmol) was added to a C₆D₆ (0.7mL) solution of (13) (1 mg, 2 μmol) in an NMR tube. The reaction wasmonitored by ¹H NMR and conversion to cyclopentanone was judged completeafter 1 h (compared to an authentic sample). Compound (13) was shown tobe a very active catalyst for the intramolecular hydroacylation of4-methyl-4-pentenal to 3-methylcyclopentanone (95% ¹H NMR, 0.5 mol % of(13), 1 h).

[0145] All patents, publications, and other published documentsmentioned or referred to in this specification are herein incorporatedby reference in their entirety.

[0146] It is to be understood that while the invention has beendescribed in conjunction with the preferred specific embodiments hereof,the foregoing description, as well as the examples which are intended toillustrate and not limit the scope of the invention, it should beunderstood by those skilled in the art that various changes may be madeand equivalents may be substituted without departing from the scope ofthe invention. Other aspects, advantages and modifications will beapparent to those skilled in the art to which the invention pertains.

[0147] Accordingly, the scope of the invention should therefore bedetermined with reference to the appended claims, along with the fullrange of equivalents to which those claims are entitled.

We claim:
 1. A compound having the formula:

wherein: R¹ and R² are independently selected from the group consistingof alkyl and aryl; Y is selected from the group consisting of P and N;and R³, R⁴, R⁵ and R⁶ are independently selected from the groupconsisting of alkyl and aryl.
 2. The compound of claim 1 wherein Y is P.3. The compound of claim 2 wherein R¹ and R² are phenyl and R³, R⁴, R⁵and R⁶ are phenyl.
 4. The compound of claim 2 wherein R¹ and R² are3-methylphenyl and R³, R⁴, R⁵ and R⁶ are phenyl.
 5. The compound ofclaim 2 wherein R¹ and R² are 3-t-butylphenyl and R³, R⁴, R⁵ and R⁶ arephenyl.
 6. The compound of claim 2 wherein R¹ and R² are 3-methoxyphenyland R³, R⁴, R⁵ and R⁶ are phenyl.
 7. The compound of claim 2 wherein R¹and R² are 2,4-di(trifluoromethyl)phenyl and R³, R⁴, R⁵ and R⁶ arephenyl.
 8. The compound of claim 2 wherein R¹ and R² are1,2,3,4,5-pentafluorophenyl and R³, R⁴, R⁵ and R⁶ are phenyl.
 9. Thecompound of claim 2 wherein R¹ and R² are phenyl-d₅ and R³, R⁴, R⁵ andR⁶ are phenyl.
 10. The compound of claim 2 wherein R¹ and R² are phenyland R³, R⁴, R⁵ and R⁶ are t-butyl.
 11. The compound of claim 2 whereinR¹ and R² are is 3-t-butylphenyl and R³, R⁴, R⁵ and R⁶ are t-butyl. 12.The compound of claim 2 wherein R¹ and R² are is phenyl and R³, R⁴, R⁵and R⁶ are methyl.
 13. The compound of claim 2 wherein R¹ and R² are isphenyl and R³, R⁴, R⁵ and R⁶ are 3-t-butylphenyl.
 14. The compound ofclaim 2 wherein R¹ and R² are is phenyl and R³, R⁴, R⁵ and R⁶ are2,4-di(trifluoromethyl)phenyl.
 15. The compound of claim 1 wherein Y isN.
 16. The compound of claim 15 where R¹ and R² are phenyl; and R³, R⁴,R⁵ and R⁶ are methyl.
 17. The compound of claim 15 where R¹ and R² arephenyl; and R³, R⁴, R⁵ and R⁶ are isobutyl.
 18. The compound of claim 15where R¹ and R² are phenyl; and R³, R⁴, R⁵ and R⁶ are t-butyl.
 19. Thecompound of claim 15 where R¹ and R² are phenyl; and R³, R⁴, R⁵ and R⁶are penyl.
 20. A zwitterionic complex of the formula:

wherein: R¹ and R² are independently selected from the group consistingof alkyl and aryl; Y is selected from the group consisting of P and N;R³, R⁴, R⁵ and R⁶ are independently selected from the group consistingof alkyl and aryl; Z is a metal; and R⁷ and R⁸ are independentlyselected from the group consisting of halo, pseudo-halo, alkyl, aryl andmono or bidentate, displaceable neutral donor ligands.
 21. The complexof claim 20 wherein Z is selected from the group consisting of titanium,zirconium, hafnium, manganese, rhenium, iron, ruthenium, osmium, cobalt,rhodium, iridium, nickel, palladium, platinum, and aluminum.
 22. Thecomplex of claim 21 wherein Z is selected from the group consisting ofnickel, palladium, and platinum.
 23. The complex of claim 21 wherein Zis selected from the group consisting of cobalt, rhodium and iridium.24. The complex of claim 20 wherein R¹ and R² are phenyl; R³, R⁴, R⁵ andR⁶ are phenyl; and Y is P.
 25. The complex of claim 24 wherein Z isnickel.
 26. The complex of claim 24 wherein Z is palladium or platinum.27. The complex of claim 24 wherein Z is rhodium.
 28. The complex ofclaim 20 wherein R⁷ is a mono or bidentate, displaceable neutral donorligand.
 29. The complex of claim 28 wherein R⁸ is a mono or bidentate,displaceable neutral donor ligand.
 30. The complex of claim 20 whereinthe mono or bidentate, displaceable neutral donor ligand is selectedfrom the group consisting of acetone, acetonitrile, olefin adducts,carbon monoxide, pyridine, tertiary phosphines, tertiary amines anddiethyl ether.
 31. A zwitterionic complex of the formula III:

wherein: R¹ and R² are independently selected from the group consistingof alkyl and aryl; Y is selected from the group consisting of P and N;R³, R⁴, R¹ and R⁶ are independently selected from the group consistingof alkyl and aryl; Z is a metal; and R⁷ is selected from the groupconsisting of halo, pseudo-halo, alkyl, aryl and mono or bidentate,displaceable neutral donor ligands.
 32. The complex of claim 31 whereinZ is selected from the group consisting of titanium, zirconium, hafnium,manganese, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium,nickel, palladium, platinum, and aluminum.
 33. The complex of claim 31wherein Z is selected from the group consisting of nickel, palladium,and platinum.
 34. The complex of claim 31 wherein Z is selected from thegroup consisting of cobalt, rhodium and iridium.
 35. The complex ofclaim 31 wherein R¹ and R² are phenyl; R³, R R⁵ and R⁶ are phenyl; and Yis P.
 36. The complex of claim 35 wherein Z is nickel.
 37. The complexof claim 35 wherein Z is palladium or platinum.
 38. The complex of claim35 wherein Z is rhodium.
 39. The complex of claim 31 wherein R⁷ is amono or bidentate, displaceable neutral donor ligand.
 40. The complex ofclaim 39 wherein the mono or bidentate, displaceable neutral donorligand is selected from the group consisting of acetone, acetonitrile,olefin adducts, carbon monoxide, pyridine, tertiary phosphines, tertiaryamines and diethyl ether.
 41. A method of catalyzing a reaction whereintransformation of a robust sigma bond in an organic compound isrequired, comprising: a) contacting the organic compound with i) anorganic or inorganic reagent, and ii) a zwitterionic complex of ananionic borate ligand having the formula:

 and a metal compound; wherein: R¹ and R² are independently selectedfrom the group consisting of alkyl and aryl; Y is selected from thegroup consisting of P and N; and R³, R⁴, R⁵ and R⁶ are independentlyselected from the group consisting of alkyl and aryl; and b) producingan organic compound having a transformed robust sigma bond.
 42. Themethod of claim 41 wherein the zwitterionic complex has the formula:

wherein: Z is a metal; and R⁷ and R¹ are independently selected from thegroup consisting of halo, pseudo-halo, alkyl, aryl and mono orbidentate, displaceable neutral donor ligands.
 43. The method of claim41 wherein the zwitterionic complex has the formula:

wherein: Z is a metal; and R⁷ is selected from the group consisting ofhalo, pseudo-halo, alkyl, aryl and mono or bidentate, displaceableneutral donor ligands.
 44. The method of claim 41 wherein the robustsigma bond is an E—H bond where E is selected from the group consistingof C, B, Si, N, H and O.
 45. The method of claim 44 wherein the robustsigma bond is a C—H bond.
 46. The method of claim 44 wherein thereaction is benzene C—H activation.
 47. The method of claim 44 whereinthe reaction is a polymerization reaction.
 48. The method of claim 47wherein the reaction is the copolymerization of ethylene and carbonmonoxide to yield —[(CH₂)₂—(CO)]_(n)—.
 49. The method of claim 44wherein the reaction is an organic transformation.
 50. The method ofclaim 44 wherein the reaction is an alkane activation reaction.
 51. Themethod of claim 50 wherein the reaction is a palladium or platinumcatalyzed C—H activation reaction.
 52. The method of claim 44 whereinthe reaction is an alkane functionalization reaction.
 53. The method ofclaim 52 wherein the reaction is an alkane oxidation.
 54. The method ofclaim 41 wherein the organic compound is an olefin or alkyne, and thereaction is an addition of an H—E bond, wherein the H—E bond is selectedfrom the group consisting of H—H, H—Si, H—B, H—C, and H—N.
 55. Themethod of claim 54 wherein the reaction is a hydrogenation reaction. 56.The method of claim 54 wherein the reaction is a hydrosilation reaction.57. The method of claim 54 wherein the reaction is a hydroborationreaction.
 58. The method of claim 4 wherein the reaction is ahydroacylation reaction.
 59. The method of claim 41 wherein the reactionis the selective activation of sp³-hybridized bonds.